In an article entitled "Inverse Cassegranian Systems" by Seymour Rosin, appearing at page 1483 in Applied Optics, August, 1968, volume 7, number 8, there is described a two mirror system in FIG. 15. This system is described as a spherically corrected inside-out system, no obscuration. The system has a magnification of 3.73205. It comprises a large concave mirror and a small convex mirror both having small apertures in the center. The object is at the apex of the large concave mirror and is imaged at the apex of the small concave mirror. The mirrors have equal radii and are separated by a distance equal to 0.866 times their radii.
Rosin's system can be represented in FIG. 1 by convex mirror 10 and concave mirror 12 having equal radii and separated by 0.866 times that radius. Reversing the object and image planes from that described in Rosin, an image 14 at the vertex of mirror 10 will be imaged at 16 at the vertex of mirror 12. The magnification will be 3.73205. Mirrors 10 and 12 are spherical. When the radii of mirrors 10 and 12 are equal, there is always a mirror separation that will give the imaging relationship just described. Rosin discovered that for this case of equal radii and vertex to vertex imaging the third order spherical aberration is zero. Since the radii are equal and opposite the Petzval curvature is also zero. The system disclosed by Rosin has coma and astigmatism.